Sleep swelling?

My DD wakes up every morning with her face very swollen. I always assumed that it was just from sleep, as my eyes are puffy when I wake up, too. But she's swollen clear down through her jaw.

My mom suggested that maybe she's allergic to something in the room, but the only thing that could be would be the cats, and she's fine being around them throughout the day. And she has no other known allergies.

Does anyone else's DD/DS wake up swollen like this? Is it just sleep? Or should I worry that it's something more?

Thanks! I asked the doc, he said "it's allergies" and wrote a prescription. Didn't ask about what's in the room with her or ask any details on it or anything. I think it's time for a new pediatrician. This isn't the first time he's done something like this. He tends to write prescriptions without telling me why or what they're for.